This project consists of five inter-related studies of B cell structure and function. Two studies address the expression of immunoglobulin genes, specifically the signals and molecular basis of isotype switching and the role of antigen structure and accessory signals needed to induce somatic variation of immunoglobulin. Projects examining non-immunoglobulin molecules in B cell function include molecular and functional studies of the cell surface glycoprotein which is the earliest marker for activated human B cells and studies designed to clone the gene for the human homolog of the mouse minor lymphocyte stimulating (Mls) antigen, a potent stimulator of T cells, and the human Fc receptor gene. both studies of human cells will pursue parallel molecular cloning strategies. Finally, B cell structures permitting or enhancing antigen presentation will be delineated and the basis for idiotype specific stimulation of T cells investigated. This program project brings together a group whose members had diverse training in virolory, molecular biology, biochemistry and cellular immunology yet share a common interest in B cell biology.